Statoil plugging unstable North Sea platform well

* Well pressure stable but not normalised - Statoil

* 1 of 2 cement plugs in place - Statoil

* Production cut by 60-70,000 boe per day

* Still unclear when production will resume

By Gwladys Fouche

OSLO, June 2 (Reuters) - Norwegian oil firm Statoil (STL.OL) said on Wednesday it had begun to pour concrete into a well that shut the North Sea Gullfaks C platform but it did not know when production would resume.

The platform was evacuated of non-essential personnel on May 20 after changes in well pressure led to a fault on one of two valves designed to prevent a blowout. [ID:nLDE64K06F]

"The first cement plug is in place. We are working towards the next step, the second plug," Statoil spokesman Gisle Johanson said. "The pressure situation is stable but it is not normalised."

The spokesman did not know how long the process would take.

"The production is still shut in and will be so until the situation is normalised," Johanson said.

Gullfaks C is one of three platforms at the site, which handles oil and gas from the Gimle, Tordis, Vigdis, Visund, Gullfaks and Gullfaks Soer fields.

Production at the small Tordis and Gimle fields are also shut, curtailing production by some 60,000 to 70,000 barrels of oil per day, Statoil said.

Gullfaks produces 78,000 barrels of oil per day and 420 million standard cubic metres of gas per year, and Tordis 46,000 barrels of oil per day and 50 million standard cubic metres of gas per year. Gimle produces 10,000 barrels of oil per day.

Some 90 people were evacuated from the platform on May 20. About 130 essential staff remain on the platform.

"We will have reduced manning until the situation is normalised," Johanson said.

Statoil owns 70 percent in Gullfaks, and Norwegian state-owned firm Petoro owns the rest.

A leading Norwegian green group, Bellona, has highlighted the risks of offshore oil and gas exploration after BP's (BP.L) well blowout and massive oil spill in the Gulf of Mexico. [ID:nSPILL]

(Editing by Sue Thomas)